Loans - Recorded Investment Based on Payment Activity (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Non-PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 6,485,532	$ 6,220,351
Non-PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,770,500	3,682,984
Non-PCI Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	382,079	371,340
Non-PCI Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,436,313	1,319,206
Non-PCI Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	896,640	846,821
Non-PCI Loans | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,469,710	6,204,779
Non-PCI Loans | Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,756,728	3,670,067
Non-PCI Loans | Performing Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	380,454	369,184
Non-PCI Loans | Performing Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,436,106	1,319,126
Non-PCI Loans | Performing Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	896,422	846,402
Non-PCI Loans | Non-Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	15,822	15,572
Non-PCI Loans | Non-Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	13,772	12,917
Non-PCI Loans | Non-Performing Loans | Consumer | Home equity
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	1,625	2,156
Non-PCI Loans | Non-Performing Loans | Consumer | Automobile
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	207	80
Non-PCI Loans | Non-Performing Loans | Consumer | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	218	419
PCI Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,537,168	4,190,086
PCI Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	362,831	428,416
PCI Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	120,144	160,263
PCI Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	657,544	740,657
PCI Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,244,129	2,494,966
PCI Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	152,520	365,784
PCI Loans | Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	3,473,646	4,133,961
PCI Loans | Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	356,413	421,609
PCI Loans | Performing Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	117,664	158,502
PCI Loans | Performing Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	628,545	710,045
PCI Loans | Performing Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,221,154	2,478,990
PCI Loans | Performing Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	149,870	364,815
PCI Loans | Non-Performing Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	63,522	56,125
PCI Loans | Non-Performing Loans | Residential mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,418	6,807
PCI Loans | Non-Performing Loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,480	1,761
PCI Loans | Non-Performing Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	28,999	30,612
PCI Loans | Non-Performing Loans | Commercial real estate | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	22,975	15,976
PCI Loans | Non-Performing Loans | Commercial real estate | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 2,650	$ 969